A comprehensive structural analysis of relaxor ferroelectric Cr- and Ni-doped Sr_0.61Ba_0.39Nb₂O₆ crystals

A structural features, real compositions, and point defects of nominally pure and Cr- and Ni-doped Sr_0.61Ba_0.39Nb₂O₆ (SBN) crystals, which structure contains four chemically-different and ten crystallochemically-different atoms, have been determined using neutron, X-ray single crystal, X-ray powder, and X-ray synchrotron diffraction techniques, and EXAFS/XANES spectroscopy. The location of transition metal ions has been identified based on the analysis of electron (nuclear) density and confirmed by the EXAFS/XANES together with the definition of formal charges of Ni atoms in Ni-doped SBN crystals. The scope and application possibilities of diffraction methods and EXAFS/XANES spectroscopy for the determination of structural features and defect formation in functional bulk nominally-pure and Cr- and Ni-doped Sr_0.61Ba_0.39Nb₂O₆ single crystals is established. - Highlights: • Undoped SBN, SBN:Cr, and SBN:Ni crystals were grown by the Stepanov technique. • Crystal structure was refined by X-ray, neutron diffraction, synchrotron radiation. • The real compositions, point defects, and location of impurities were refined. • The presence of Ni²⁺ and Ni³⁺ ions in the vicinity of Nb1 site was found by EXAFS. • The limits of applicability of methods and techniques were determined.